The use of hydrostatic transmissions (“HSTs”), including integrated hydrostatic transmissions (“IHTs”), are well known in the art for use with self-propelled vehicles such as tractors, riding lawn mowers, self-propelled lawn mowers, and the like. HSTs are fully described for example in U.S. Pat. Nos. 5,819,537, 5,335,496 and 5,163,293, each of which is incorporated by reference herein in its entirety.
Generally, an HST includes at least one hydraulic pump and at least one hydraulic motor, each having a cylinder block with reciprocating pistons. The pistons of a hydraulic pump are fluidly connected to the pistons of a hydraulic motor, for example through hydraulic fluid lines or a center section on which one or more of the pump and motor are mounted. The pump is generally driven by a prime mover, such as a typical combustion engine. The pump transfers power to the hydraulic motor which is coupled to one or more axles of a vehicle, such as those described above. A movable swash plate abuts against the tops of the pump pistons which controls the movement of the pistons within the cylinder block. The slant of the swash plate controls the amount and direction of hydraulic fluid discharged from the pump to the motor. When the swash plate is moved in a first direction, the discharged hydraulic fluid is channeled to the motor in a first direction, which in turn drives the wheels of the vehicle in a first driving direction. When the swash plate is moved in a second direction, the discharged hydraulic fluid is channeled to the motor in a second direction, which in turn drives the motor in a second driving direction opposite of the first driving direction. The swash plate also has a neutral position, wherein the swash plate is not tilted. In this neutral position, the pump does not discharge hydraulic fluid, the motor does not operate and the wheels do not move, even though the prime mover is powering the hydrostatic transmission. The movable swash plate is tilted by a trunnion arm which is connected to a control shaft for controlling the position of the movable swash plate, and thus the speed and direction of the hydraulic motor. The control shaft is usually turned by a control arm linked to an input device, such as a lever or pedal for a user to operate the vehicle.
As a safety precaution, HSTs conventionally have an automatic return-to-neutral mechanism, such as a spring-loaded control arm. When the operator is not physically moving the input device, the control arm is automatically returned to a neutral position and the vehicle is stopped. However, when the vehicle is being used for an extended period of time, it can be arduous for a user to hold the input device in an operating position in order to overcome the automatic return-to-neutral feature.
Thus, various cruise control devices have been developed to keep a control arm in an operating position for an extended period of time. However, many of these cruise control devices are very complex and require the cruise control device to overcome or to disable the force of a return-to-neutral system in order to hold the control arm in position. Also adding to the complexity, braking systems are necessary to disable the cruise control feature such that the conventional automatic return-to-neutral mechanism will return the control arm to a neutral position and thus stop the operation of the vehicle.
Thus, a more simple apparatus is desired to hold a control arm in position and to stop the operation of a vehicle when desired.